You've reached the Virginia Cooperative Extension Newsletter Archive.
These files cover more than ten years of newsletters posted on our old website
(through April/May 2009), and are provided for historical purposes only.
As such, they may contain out-of-date references and broken links.

High levels of potato leafhopper already present in Virginia alfalfa

Potato leafhopper populations are weeks ahead of their normal levels, and
are approaching threshold levels in some fields, especially in the
Piedmont. Alfalfa fields in Augusta, Campbell, Montgomery, Orange, and
Rockbridge Counties were sampled for potato leafhopper between June 1 and
5. Alfalfa stem length in these fields ranged from 6 to 18 inches.
Leafhopper populations ranged from 0.3 per sweep in Montgomery County to
1.0 per sweep in Orange County. The action threshold changes depending on
stem length, so taller alfalfa can withstand higher numbers of potato
leafhoppers.

Almost all the potato leafhoppers counted were adults, which tells us that
high numbers of eggs are being deposited. These eggs will be hatching in
the next few weeks and we expect very high numbers of nymphs to start
feeding. Nymphs are already present in Orange County. Damage to alfalfa
may be severe, especially to fields that are just now being harvested.
Fortunately, second-cutting alfalfa regrowth has been excellent. Growers
are advised to monitor all alfalfa fields for potato leafhopper,
especially those fields that have recently been cut. Procedures for
monitoring potato leafhopper and recommended insecticides for controlling
this insect are described on pages 126-128 of the 2000 Virginia Pest
Management Guide for Field Crops-Extension Publication no. 456-016 (or go
to http://www.ext.vt.edu/pubs/pmg/fc4a.pdf
to download a PDF file of the
Field Crops Insects section from the Pest Management Guide-then scroll
down to page 126).

With plenty of soil moisture allowing rapid growth, alfalfa may soon reach
the point at which spraying to control potato leafhopper is considered
uneconomical. Any alfalfa that is taller than 14 inches and has leafhopper
levels exceeding the thereshold should be harvested early rather than
sprayed.